Lord Mandelson, a former Labour Cabinet minister, told the House of Lords that “no empirical case has been established for HS2”.

“I have been an ardent pro-railway supporter all my adult life. But it is precisely for that reason that I do not support HS2," Lord Mandelson said.

“I think the sheer cost of it will suck the very life blood out of the rest of the country's rail system.”

He acknowledged that while in government he had supported HS2, but said that Labour was now right to have become more sceptical.

"Frankly there was too much of the argument that if everyone else had got a high speed train we should have one too - regardless of costs and alternatives," he said.

Lord Mandelson said there were dozens of transport projects urgently needed across the country which would make a "very significant economic and social impact" and could be "extracted" from the HS2 price tag.

He warned that if the project went ahead there would be nearly £8 billion of cuts in the existing intercity network.

"If this goes ahead we will see a shrinking of the rail network in this country and that should be the very last thing pro-rail supporters would want to see," he said.

HS2 is a "political trophy project justified on flimsy evidence to be about modernity and prosperity”, Lord Mandelson added.

Lord Rooker, a former Labour minister, attacked Lord Mandelson and said he was getting "cheesed off" listening to former members of the government "pouring cold water" on the project.

"The Labour government started this project and it will be inconceivable to withdraw support," Lord Rooker said.

"I am getting cheesed off listening to ex ministers swanning around the political salons pouring cold water on this project."

"I urge the shadow cabinet not to quit on the project but to fight for it. I urge HS2 to get its communications and operations a bit more transparent."

He added: "In the days of the great engineering projects approved in private bills by this Parliament the likes of Brunel and Telford got on with their vision and they won through in the end and thank goodness they did.

"They would be ashamed and astonished to see us today - a scrimping nation getting by, or at least we think we are."

A Downing Street spokesman said: "The Prime Minister's position on HS2 is well-stated. We need to invest in high-speed rail in this country.

"It is essential for solving the capacity crisis and research from KPMG has shown there could be a £15 billion annual boost to the economy.

"The Prime Minister is clear in his support for HS2 and wants the process to go on and the railway to be built. There will be a vote next week, which the Government will be going out and supporting to get this thing delivered."